Question

A woman with two gases (one on each X-chromosome) for haemophilia and one gene for colour blindness on the X-chromosomes marries a normal man. How will the progeny be?
A. All sons and daughters haemophilic and colour blind
B. Haemophilic and colour blind daughters
C. 50% haemophilic colour blind sons and 50% haemophilic sons
D. 50% haemophilic daughters and 50% colour blind daughters

Answer 1

Correct Answer - C
Haemophilia and colour blindness both are recessive X-linked traits. They express in males when present in single copy (heterozygous) but in females they express only when present in homozygous condition.

Results
(a) 50% sons are colour blinds and haemophilic.
(b) 50% sons are haemophilic only.
(c ) 50% daughters are carrier for colour blindness and haemophilia.
(d) 50% daughters are carrier for haemophillia only.